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分数应用题是教材中的重点和难点,在教学中为突破这一重、难点,用线段图分析题中的数量关系,是一种比较行之有效地办法.而且通过线段图的分析,其解法可有多种.例1 小红家买来大米和面粉84千克,其中面粉是大米的2/5.大米和面粉各买来多少千克?首先,根据题中条件画出线段图:(1)从图上看出:在84千克粮食里,大米有5份,面粉有2份,一共是7份.用比例分配方法可得:①总份数:5+2=7②大米的千克数:84×5/7=60(千克)③面粉的千克数:84×2/7=24(千克)(2)从图中看出:84千克的对应分率是(1+2/5).可根据分数除法的意义可列式:大米:84÷(1十2/5)=60(千克)
Application of the score is the teaching material in the key and difficult point in teaching to break through this heavy, difficult, with the number of line segments analysis of the relationship between the number of questions is a more effective way .And through the analysis of the line graph, the solution Example 1 Xiao Hongjia bought 84 kilograms of rice and flour, of which flour is 2/5 of rice. How many kilograms of rice and flour each bought? First of all, according to the conditions of the drawing line segment: (1) It can be seen from the figure that in 84 kg of grain, there are 5 portions of rice and 2 portions of flour, for a total of 7. The proportion distribution method can be used to obtain: ① total portions: 5 + 2 = 7 ② kilograms of rice: 84 × 5/7 = 60 (kg) ③ kg of flour: 84 × 2/7 = 24 (kg) (2) As can be seen from the figure, the corresponding fraction of 84 kg is (1 + 2/5) According to the meaning of fractional divisible formula: Rice: 84 ÷ (1 ten 2/5) = 60 (kg)